From Easy Going Scans:

Liola—the best assassin in his world—has vowed to kill no more. He was being chased by an assassination organization when he accidentally dropped into a parallel universe: through a dimensional gate and into poor teenager Kaiser's apartment.

Liola has been trying his best to live the life of an ordinary person, but after certain things happen one after the other, he begins to realize that being an ordinary person could be harder than being an assassin.